U.S. patent number 5,150,260 [Application Number 07/769,453] was granted by the patent office on 1992-09-22 for optical apparatus.
This patent grant is currently assigned to Canon Kabushiki Kaisha. Invention is credited to Tatsuo Chigira.
United States Patent |
5,150,260 |
Chigira |
September 22, 1992 |
Optical apparatus
Abstract
An optical apparatus comprises a lens holding member holding a
lens, a guide member for guiding the movement of the lens holding
member in the direction of the optical axis, a gear shaft rotatable
by a drive source, and a moving member having a gear portion
meshing with the gear shaft and movable in the direction of the
optical axis by the rotation of the gear shaft to thereby move the
lens holding member in the direction of the optical axis, the
moving member being supported for rotation in a direction
substantially orthogonal to the axial direction of the gear
shaft.
Inventors: |
Chigira; Tatsuo (Yokohama,
JP) |
Assignee: |
Canon Kabushiki Kaisha (Tokyo,
JP)
|
Family
ID: |
17415971 |
Appl.
No.: |
07/769,453 |
Filed: |
October 1, 1991 |
Foreign Application Priority Data
|
|
|
|
|
Oct 2, 1990 [JP] |
|
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2-265351 |
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Current U.S.
Class: |
359/694; 359/696;
359/823; 396/89 |
Current CPC
Class: |
G02B
7/08 (20130101) |
Current International
Class: |
G02B
7/08 (20060101); G02B 015/00 () |
Field of
Search: |
;359/694,696,823,825,829,830 ;354/195.1,286,400 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Ben; Loha
Attorney, Agent or Firm: Robin, Blecker, Daley &
Driscoll
Claims
What is claimed is:
1. An optical apparatus comprising:
a lens holding member holding a lens;
a guide member for guiding the movement of said lens holding member
in the direction of an optical axis;
a gear shaft rotatable by a drive source; and
a moving member having a gear portion meshing with said gear shaft
and movable in the direction of the optical axis by the rotation of
said gear shaft to thereby move said lens holding member in the
direction of the optical axis, said moving member being rotatably
supported in a direction substantially orthogonal to the axial
direction of said gear shaft.
2. An optical apparatus according to claim 1, further
comprising:
biasing means for biasing said gear portion in said moving member
to said gear shaft.
3. An optical apparatus according to claim 2, wherein a guide shaft
is used as said guide member, and said moving member is rotatably
supported relative to said guide shaft.
4. An optical apparatus according to claim 1, wherein a guide shaft
is used as said guide member, and said moving member is rotatably
supported relative to said guide shaft.
5. An optical apparatus according to claim 4, wherein said lens
holding member bears against said moving member, and when said
moving member is moved in the direction of the optical axis, said
lens holding member is pushed thereby and moved in the direction of
the optical axis.
6. An optical apparatus according to claim 1, wherein said lens
holding member bears against said moving member, and when said
moving member is moved in the direction of the optical axis, said
lens holding member is pushed thereby and moved in the direction of
the optical axis.
7. An optical apparatus according to claim 1, wherein said moving
member is rotatably supported relative to said lens holding
member.
8. An optical apparatus according to claim 7, wherein said lens
holding member bears against said moving member, and when said
moving member is moved in the direction of the optical axis, said
lens holding member is pushed thereby and moved in the direction of
the optical axis.
9. An optical apparatus according to claim 2, wherein said moving
member is rotatably supported relative to said lens holding
member.
10. An optical apparatus according to claim 2, wherein a spring is
used as said biasing means, and said spring is fixed to said moving
member.
11. An optical apparatus according to claim 2, wherein a spring is
used as said biasing means, and said spring is formed integrally
with said moving member.
12. An optical apparatus according to claim 1, wherein said moving
member is formed with a plurality of gear portions, and is brought
into meshing engagement with said gear shaft at a plurality of
locations.
13. An optical apparatus according to claim 2, wherein said moving
member is formed with a plurality of gear portions, and is brought
into meshing engagement with said gear shaft at a plurality of
locations, and said biasing means biases said plurality of gear
portions against said gear shaft at a location between said
plurality of gear portions.
14. An optical apparatus according to claim 13, wherein a spring is
used as said biasing means, and said spring is fixed to said moving
member.
15. An optical apparatus according to claim 13, wherein a spring is
used as said biasing means, and said spring is formed integrally
with said moving member.
16. An optical apparatus according to claim 1, wherein a rack is
used as said moving member.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an optical apparatus having a lens
driving device.
2. Related Background Art
Auto focus mechanisms in photo-taking lenses for video cameras have
heretofore included an auto focus device which emits infrared light
and meters light impinging on and reflected by an object, and an
auto focus mechanism which meters the contrast of light passed
through a photo-taking optical system by a CCD (solid state image
pickup element) and judges in-focus by the value of the contrast
having reached a peak. Any of these is such that a focusing lens is
driven by an actuator in accordance with instructions from a
distance measuring device to thereby perform the focusing
operation.
Particularly in the latter auto focus device of the contrast
detection type, the combination thereof with an inner focus optical
system which pursues the compactness of the optical system has
often been seen in recent years. As an example of the prior art, as
shown in FIG. 5 of the accompanying drawings, a focusing lens
holding frame 200 is designed to be parallel-movable in the
direction of the optical axis by two guide shafts 300 and 400. A
rack 500 meshing with a lead screw 800 formed on the shaft of a
stepping motor 900 is mounted on a portion of the lens holding
frame 200.
However, according to such structure, if the two guide shafts 300
and 400 for moving the lens are not parallel to the lead screw 800
which is the shaft of the stepping motor 900, an angular movement
is created in the rack 500, whereby the movement of the lens
holding frame 200 becomes unsmooth. Therefore, in order to ensure
the degree of parallelism of these members, it has been practised
to increase the accuracy of the parts or provide a mechanism for
adjustment. As a result, a long time has been required for
assembly, or a highly accurate and expensive part molding machine
has been necessary to increase the accuracy of the parts.
So, in order to solve such problems, there has been devised a
device as disclosed in Japanese Laid-Open Utility Model Application
No. 2-71155 (its corresponding U.S. Patent has not yet been
ascertained).
This device is such that a rack and a lens holding frame are
connected together by a flexible connecting member, and the
connecting member comprises, for example, a relatively thin spring
member, and is intended to have rigidity for the movement of the
lens in the direction of the optical axis and to have flexibility
in a direction perpendicular to the optical axis.
In this device, however, to provide sufficient flexibility, it is
necessary to make the connecting member thin, and to provide
sufficient rigidity in the direction of the optical axis, it is
necessary to make the length of the connecting member sufficiently
great in the direction of the optical axis. This has led to the
problem that an optical accessory such as a lens barrel using the
device disclosed in Japanese Laid-Open Utility Model Application
No. 2-71155 becomes bulky.
SUMMARY OF THE INVENTION
One aspect of this invention is to provide an optical apparatus in
which a lead screw rotated by a drive screw, a rack gear portion
meshing with the lead screw and a biasing portion for biasing the
rack gear portion toward the lead screw are provided as a lens
driving device for moving a lens in the direction of the optical
axis, the rack gear portion being supported for rotation in a
direction substantially orthogonal to the axial direction of the
lead screw, whereby the movement of the lens can be accomplished
smoothly.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side view, partly in cross-section, showing the general
construction of a first embodiment of the present invention.
FIG. 2 is a perspective view of the essential portions of FIG.
1.
FIG. 3 is a cross-sectional view showing a second embodiment of the
present invention.
FIG. 4 is a perspective view showing a third embodiment of the
present invention.
FIG. 5 is a perspective view showing a lens driving device
according to the prior art.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Some embodiments of the present invention will hereinafter be
described with reference to the drawings. FIG. 1 is a side view,
partly in cross-section, for illustrating the general construction
of an embodiment using a lens barrel for a video camera as an
optical apparatus.
In FIG. 1, the reference numeral 1 designates a lens barrel body in
which a zoom lens optical system of rear focus is contained. The
reference numeral 2 denotes a focusing lens holding frame supported
for movement in the direction of the optical axis relative to a
guide shaft 3 parallel to the optical axis. The reference numeral 4
designates a guide shaft also parallel to the optical axis. The
guide shaft 4 regulates the rotation of the lens holding frame 2.
The reference numeral 5 denotes a rack meshing with a lead screw 8
which provides the output shaft of a motor 9. The reference numeral
10 designates a CCD lying at the imaging position of the optical
system.
The details of a lens driving portion which is the focus mechanism
portion of FIG. 1 will now be described with reference to the
perspective view of FIG. 2.
In FIG. 2, the letter G designates a focusing lens held by the lens
holding frame 2, which in turn is supported on the guide shaft 3
parallel to the optical axis by a sleeve portion 2a, and a U-shaped
guide portion 2b has its rotation regulated by the guide shaft 4
parallel to the optical axis. The reference numeral 5 denotes a
rack having rack gear portions 5a and 5b. The rack 5 embraces the
right and left parts of the sleeve portion 2a of the lens holding
frame 2 without any back-lash and is movable in the direction of
the optical axis along the guide shaft 3 with the lens holding
frame 2.
Further, an L-shaped leaf spring 6 is attached to the rack 5 by
means of a screw 7, and the lead screw 8 which is a motor shaft is
resiliently embraced by the rack gear portions 5a, 5b and the leaf
spring 6. The thread pitch of the lead screw 8 coincides with the
pitches of the rack gear portions 5a and 5b, and the rotation of
the lead screw 8 moves the rack 5 in the direction of the optical
axis. The reference numeral 9 designates a stepping motor for
driving the focusing lens G. The stepping motor 9 has the lead
screw 8 and is held by a substantially U-shaped fitting 14. A
bearing 11 is secured to the substantially U-shaped fitting 14 and
regulates the rotation of the lead screw 8 and the position thereof
in the thrust direction. The reference numeral 12 denotes a cable
for supplying electric power to the motor 9, and the reference
numeral 13 designates a connector.
The operation of the present embodiment will now be described. A
so-called auto focus device (not shown) for detecting the degree of
blur of an image formed on the CCD 10 and instructing a focusing
lens driving motor to rotate in conformity with the degree of blur
and the motor 9 are coupled together by the connector 13 and the
cable 12.
The lead screw 8 of the motor 9 is rotated by an amount of rotation
designated by an auto focus distance measuring device. The rack
portions 5a and 5b meshing with the lead screw 8 are moved axially,
whereby the rack 5 sleeve-fitted to the guide shaft 3 and disposed
parallel to the lead screw 8 is moved parallel to the optical axis.
Further, the lens holding frame 2 is supported by the guide shaft 3
and is held between the cut-away portions of the rack 5 and
therefore, can be moved in a direction parallel to the optical axis
without any back-lash. On the other hand, the guide shaft 4 has its
rotation regulated by the U-shaped portion 2b of the lens holding
frame 2 and thus, by the rack 5 being moved in the direction of the
optical axis, the focusing lens G mounted on the lens holding frame
2 is moved in the direction of the optical axis. At this time, the
rack gear portion 5a and the lead screw 8 are pressed by the leaf
spring 6 and therefore can mesh with each other without any
back-lash. Also, the rack 5 is supported on the guide shaft 3 for
movement in the direction of the optical axis and therefore, even
if the degree of parallelism of the guide shaft 3 and the lead
screw 8 is more or less inaccurate, the rack 5 will be rotated
about the guide shaft 3, whereby an inconvenience such as being
caught during movement will be prevented from occurring.
That is, even if the lead screw 8 has a degree of parallelism to
the guide shafts 3 and 4 resulting in an optical performance that
is more or less inaccurate, the movement of the lead screw will be
affected in no way. Generally, the motor 9 is mounted after the
assemblage of the optical system and thus, the motor 9 can be
mounted without being adjusted in any way at that time. Of course,
if the degree of parallelism of the guide shaft 3 and the lead
screw 8 is greatly inaccurate, it will pose a problem, but
generally, the degree of parallelism will be inaccurate by only the
order of 1.degree.-2.degree. even if the motor is mounted without
any care. For such degree of inaccuracy of the degree of
parallelism, the amount of variation in the focusing lens G in the
direction of the optical axis will be only sin 1.degree.-2.degree.
and will hardly pose a problem.
Also, in the present embodiment, the center of rotation of the rack
5 and the center of holding of the lens holding frame 2 are coaxial
with the guide shaft 3, but in principle, the rotary shaft of the
rack 5 parallel to the optical axis may be provided on a portion of
the lens holding frame 2.
FIG. 3 is a cross-sectional view showing a second embodiment of the
present invention.
As shown in FIG. 3, in this embodiment, a rack 51 is not directly
fitted to a guide shaft 31, but is rotatably fitted to a lens
holding frame 21. The lens holding frame 21 is supported relative
to the guide shaft 31 by a sleeve 21a and is parallel-movable in
the direction of the optical axis. Bosses 21e and 21f are provided
on the outer periphery of the sleeve 21a and are rotatably fitted
to each other with the aid of holes 51c and 51d in the rack 51.
That is, the rack 51 is rotatably supported relative to the lens
holding frame 21. Further, the thin portion 51e of the rack 51 is
resilient in the axial direction and sandwiches the surfaces 21c
and 21d of the lens holding frame 21 by and between surfaces 51f
and 51g so that there may not be back-lash in the axial direction.
Thus, the rack 51 is free of back-lash in the direction of the
optical axis relative to the lens holding frame 21, but is freely
rotatable in a direction perpendicular to the optical axis. Of
course, the same effect will be obtained even if a resilient member
is interposed between the surfaces 51f and 21d or 51g and 21c. The
rack 51 may conceivably be converse to its shown construction in
its fitting and its portion fitted to the lens holding frame 21,
but the degree of parallelism thereof to the optical axis may be
more readily provided if the lens holding frame 21 is fitted to the
guide shaft 31.
FIG. 4 is a perspective view showing the essential portions of a
third embodiment of the present invention. In FIG. 4, portions
similar in construction to those of the first embodiment shown in
FIGS. 1 and 2 are given similar reference characters and need not
be described.
A rack 150 in this embodiment is made of a material with excellent
sliding capability such as polyacetal resin and is formed with
first and second holes 150a and 150b (of which the second hole 150b
is not shown), and the guide shaft 3 is inserted in the first and
second holes 150a and 150b. The rack 150 is also formed with a
recess 150c which is of dimensions and a shape making contact with
the direction of thickness of the lens holding frame 2 (the
direction of the optical axis). The rack 150 is provided with
first, second and third springy extensions 150d, 150f and 150h, and
rack gear portions 150e and 150g are provided on the end portions
of the first and second extensions 150d and 150f, respectively, and
are in meshing engagement with the threads of the lead screw 8. The
first, second and third extensions 150d, 150f and 150h of the rack
150 are of dimensions and a shape which nip the lead screw 8
therebetween with such a predetermined force that no back-lash
occurs in the threaded portion between the rack gear portions 150e,
150g provided on the end portions of the first and second
extensions and the third extension 150h.
In this embodiment, the springs nipping the lead screw 8
therebetween are formed integrally with the rack, whereby the lens
can be made compact, and even when the lead screw 8 is mounted on
an incline with respect to the guide shaft 3, the lead screw 8 is
mounted on an incline so that for example, the spring charge force
between the first extension 150d and the third extension 150h may
increase, whereby the spring charge force between the second
extension 150f and the third extension 150h is decreased and
therefore, there can always be provided a stable back-lash
eliminating force in the threaded portion.
In each of the above-described embodiments, the sleeve portion of
the lens holding frame and the sleeve portion of the rack are
fitted coaxially with each other and move as a unit without any
back-lash in the axial direction, but the fore end of the rack is
urged against the lead screw and can be moved to the focusing lens
without any back-lash with respect to the rack gear portion and at
the same time, the movement thereof after the assemblage can be
accomplished smoothly. Further, since the rack is rotatably
supported, any angular movement (any force with which the rack gear
portion and the lead screw contact with and separate from each
other) is not created in the rack portion. Thus, stable driving can
always be accomplished.
In each of the above-described embodiments, the rack is rotatably
supported on the lens holding frame itself or the guide shaft so
that the guide shaft becomes a rotation center, but alternatively,
the rotation center of the rack might be shifted from the guide
shaft by, for example, providing another shaft to the lens holding
frame.
As described above, in the optical apparatus having the lens
driving device according to each of the above-described
embodiments, the rack is rotatably supported in a direction
substantially orthogonal to the direction of the optical axis and
therefore, the creation of any angular movement to the rack can be
effectively prevented and the movement of the lens holding frame
can be accomplished smoothly.
Also, in each of the above-described embodiments, the rack is
rotatably supported on the guide shaft which guides the lens
holding frame or on the lens holding frame itself, whereby the
guide shaft or the lens holding frame can serve also as a shaft for
supporting the rack, and this leads to the possibility of achieving
the compactness and reduced cost of the apparatus.
* * * * *